1. Field of the Invention
The present invention relates to a production line for machining a workpiece by conveying the workpiece successively to a plurality of production devices arranged in a line.
2. Description of the Related Art
In production lines of this kind, for the purposes of changing a workpiece, performing maintenance on individual production devices, making improvements and changes to the production process, etc., the production devices are interchanged or moved out of the production line for maintenance as required. Of the production devices constituting the production line, machine tools used for cutting, grinding, or the like usually weigh on the order of several tons; as for their sizes, those machines are typically as large as 800 mm in width and 2,500 mm in depth at the minimum.
Therefore, equipment such as a crane is required for interchanging the machines, which in turn requires a large working space and a large amount of manpower, resulting in poor efficiency. Further, the production line must be stopped during the interchanging or maintenance operation; since the interchanging of the machines itself is a rather large-scale operation, the production line is stopped for a long period of time, often more than one day.
With conventional machine tools, it is possible to secure a working space inside the machines because the machines themselves are large. However, due to the miniaturization of machines in recent years, it is impossible to secure a sufficient working space inside machines, resulting in an increase in the time required for the replacement or adjustment of parts, so increasingly longer time is required in total for retooling.
Instead of providing an additional space inside the machines, the area around the machines is often utilized as the working space. However, in cases where the machines are integrated into a production line, it is necessary to provide a large spacing between the machines in order to secure a requisite working space, so the production line increases in length and the space efficiency deteriorates.
In view of this, there are various known inventions aimed at facilitating the maintenance or interchanging of production devices such as machine tools that are arranged at a narrow spacing. In JP 2002-370142 A, individual main body machines (beds, headstocks, or X-Y tool tables) are made common to one another, and a separate modular unit (tool spindle) is provided for each of the machines, thereby facilitating changes to the production process.
In JP 2002-370142 A, however, it is necessary to provide a working space for maintenance between the machines, so the line length cannot be shortened when the machines are arranged close to one another.
Further, in JP 2001-121386 A, R-type machine tools and L-type machine tools, in which an apparatus group requiring maintenance is collectively located on the right-hand and on the left-hand side, respectively, of the machine tool main body, are arranged alternately, and a maintenance space is provided for each set of two machine tool main bodies by enlarging the gap through which the apparatus groups requiring maintenance are opposed back to back to each other, with the two machine tool main bodies being held in intimate contact with each other to thereby reduce the line length.
However, when changes to the production process are effected simply by interchanging part of the machines as described in JP 2001-121386 A, the freedom of changes is somewhat limited. Further, it is often necessary to change all the machines. In order to change the whole machines, the machines must be interchanged by drawing them out of the production line altogether with their machine bases.
As described above, in conventional production lines, a space allowing the maintenance or movement of the machines in and out of the production lines must be provided between the machines, resulting in such problems as increased production line length due to the space or the necessity to draw out the entire machine, which is rather heavy and bulky, from the production line altogether with their machine bases when interchanging the machines.